In general, a double-acting fluid-pressure cylinder is long known in which two pressure chambers separated from each other by a piston have respective air-supplying/exhausting ports, and the air-supplying/exhausting ports are alternately connected to a fluid-pressure source by, for example, switching an electromagnetic valve connected to the fluid-pressure source, whereby the piston is moved back and forth with a fluid pressure applied thereto.
Typically, in such a double-acting fluid-pressure cylinder, when the piston is moved back and forth with the fluid pressure applied thereto, compressed fluid in one of the pressure chambers that is on the exhaust side is discharged to the atmosphere as the pressure chamber contracts with the movement of the piston.
From the viewpoint of energy saving, though, the compressed air that is discharged from the pressure chamber with the movement of such a fluid-pressure actuator is desirably reused as much as possible.
Accordingly, a pneumatic cylinder apparatus is proposed by PTL 1 in which exhaust air from a rod-side pressure chamber is caused to reflux into a head-side pressure chamber and is reused when a rod of a double-acting cylinder is moved forward. This apparatus employs, as a switching valve connected to a pneumatic-pressure source, a four-way two-position switching valve having a function of supplying and exhausting compressed air into and from the cylinder and a function of causing the exhaust air to reflux.